Fractionation of triglyceride oils

ABSTRACT

Fractionation of lauric oils which contain a crystallization modifying substance consisting of a sucrose ester containing at least 40 wt. % laurate. With palmkernel oil fractionation a separation efficiency of more than 70% can be attained.

This application is the national phase of international applicationPCT/EP96/01241, filed Mar. 21, 1996 which was designated the U.S.

The present invention is concerned with a process for fractionatingtriglyceride oils, particularly lauric oils. The fractionation(fractional crystallization) of triglyceride oils is described byGunstone, Harwood and Padley in The Lipid Handbook, 1986 edition, pages213-215. Generally triglyceride oils are mixtures of varioustriglycerides having different melting points. Lauric oils aretriglyceride oils which contain a considerable amount of esterifiedlauric acid, such as coconut oil (CN), palmkernel oil (PK) andderivatives thereof. The composition of triglyceride oils may bemodified e.g. by fractionation yielding a fraction having a differentmelting point or solubility.

One fractionation method is the so-called dry fractionation processwhich comprises cooling the oil until a solid phase crystallises andseparating the crystallised phase from the liquid phase. The liquidphase is denoted as olein fraction, while the solid phase is denoted asstearin fraction.

The separation of the phases is usually carried out by filtration,optionally applying some kind of pressure.

The major problem encountered with phase separation in the dryfractionation process is the inclusion of a lot of liquid olein fractionin the separated stearin fraction. The olein fraction is therebyincluded in the inter- and intracrystal spaces of the crystal mass ofthe stearin fraction. Therefore the separation of the solid from theliquid fraction is only partial.

The solids content of the stearin fraction is denoted as the separationefficiency. In dry fractionation it seldom surpasses 50 to 60 wt. %.This is detrimental to the quality of the stearin as well as to theyield of the olein. For the related solvent fractionation process, wherethe fat to be fractionated is crystallised from e.g. a hexane or acetonesolution, separation efficiencies may be up to 95%.

Dry fractionation, however, is a process which is more economical andmore environmentally friendly than solvent fractionation. For dryfractionation an increase of separation efficiency is therefore muchdesired, particularly for the commercially very important lauric oils.

It is known to interfere with the crystallization by adding to acrystallising oil a substance which will generally be indicated as acrystallization modifying substance. The presence of small quantities ofsuch a substance in the cooling oil may accelerate, retard or inhibitcrystallization. In certain situations the above substances are moreprecisely indicated as crystal habit modifiers. Known crystallizationmodifiers are e.g. fatty acid esters of sucrose, described in U.S. Pat.Nos. 3,059,010, 3,059,010, JP 05/125389 and JP 06/181686, fatty acidesters of glucose and derivatives, described in U.S. Pat. No. 3,059,011.These crystallization modifiers are effective in speeding up thecrystallization rate.

Other crystallization modifiers, e.g. as described in U.S. Pat. No.3,158,490 when added to kitchen oils have the effect that solid fatcrystallization is prevented or at least retarded. Other types ofcrystallization modifiers, particularly referred to as crystal habitmodifiers, are widely used as an ingredient for mineral fuel oils inwhich waxes are prone to crystallize at low temperatures. U.S. Pat. No.3,536,461 teaches the addition of a crystal habit modifier to fuel oilwith the effect that the cloud point (or pour point) temperature islowered far enough to prevent crystal precipitation. Or, alternatively,the solids are induced to crystallize in a different habit so that thecrystals when formed can pass fuel filters without clogging them. Othercrystal habit modifiers are actually able to change the habit of thecrystallized triglyceride fat crystals in a way such that aftercrystallization the crystals, the stearin phase, can be more effectivelyseparated from the liquid phase, the olein phase. Publicationsdescribing such crystal habit modifiers are e.g. GB 1 015 354, U.S. Pat.No. 2,610,915, co-pending PCT application WO 95/04122, U.S. Pat. Nos.3,059,008, 3,059,009 and 3,059,010.

Separation efficiency also depends on the mode of crystallisation,either stagnant or stirred. Often good results are obtained withstagnant crystallisation rather than with stirred crystallisation. Fromthe point of view of process economy, however, stirred crystallizationis preferred.

Lauric oils often crystallize in a needle-like morphology. The resultingcrystal agglomerates (see FIG. 1A) easily include olein. Fractionationby stirred crystallization is sometimes impossible because thehydrodynamic shear would crush the needles and produces crystal slurrieswhich often can be hardly or not separated in a stearin and an oleinhase. Palmkernel oil fractionation is not possible except in a stagnantmode and therefore is a very labour intensive process. For lauric oilsan effective separation efficiency enhancing substance is badly needed.

STATEMENT OF INVENTION

It has been found that the presence of a sucrose laurate in thefractionation of lauric oils causes crystallization of large andnon-porous spherulites which highly increases the separation efficiency.Accordingly the invention relates to a process for separating solidfatty material crystallised from lauric oils, which comprises the steps:

a. heating the oil until no longer a substantial amount of solidtriglyceride is present in the oil,

b. cooling and crystallising the triglyceride oil resulting in a solidstearin phase besides a liquid olein phase and

c. recovering the stearin phase by separating it from the olein phase,

where before crystallization starts a crystallization modifyingsubstance is added to said triglyceride oil or to a solution of saidtriglyceride oil in an inert solvent, characterized in that thecrystallization modifying substance is a sucrose laurate.

DESCRIPTION OF THE FIGURE

FIG. 1A shows agglomerates of needle-like crystals of palmkernel oilobtained by quiescent crystallization without additive.

FIG. 1B shows spherulite crystals of palmkernel oil obtained by stirredcrystallization in the presence of sucrose polylaurate.

DETAILS OF THE INVENTION

The lauric oil to be fractionated is mixed with the crystallizationmodifying substance (the additive) before crystallization starts,preferably before the oil is heated or dissolved in the solvent so thatall solid triglyceride fat and preferably also the modifying substanceis liquefied.

The lauric oil can be any triglyceride oil or a mixture of triglycerideoils having a content of lauric acid which is 10-75 wt. %, preferably20-60 wt. %, more preferably 30-60 wt. % calculated on total fatty acidcontent, for example coconut oil or palmkernel oil. The oils may havebeen prepared with the use of fractionation, hydrogenation or (chemicalor enzymatic) interesterification.

Sucrose laurate in the context of this description denotes a sucroseester of which on average at least four, preferably five to six of theeight hydroxyl groups have been esterified with a fatty acid. 40-100 wt.%, preferably 60-100 wt. %, more preferably 75-100 wt. % of the fattyacids should be lauric acid. The ester can be obtained by well-knownusual processes such as esterification of sucrose with a lauric acidcontaining mixture of fatty acids or of reactive fatty acid derivatives.Sucrose with more than four free hydroxyl groups has an insufficient oilsolubility. Sucrose polylaurate as mentioned in this specification is ahighly esterified (50-100%) sucrose ester with a lauric-content of 95wt. %. It is a readily available commercial product (e.g. Ryoto SugarEster L195, ex MITSUBISHI).

When the mixture of triglyceride and sucrose laurate has been liquefied,the oil or solution is cooled to the chosen crystallization temperature.A suitable temperature range is 15-35° C. To each temperature belongs aspecific composition of the olein and stearin phases. Crystallizationproceeds at the chosen temperature until the crystallised oil stabilisesto a constant solid phase content. The crystallization time increaseswhen more solid phase is desired and the temperature is lowered. Usualtimes are in the range of 4-16 hours. During crystallization the oil mayremain quiescent or is stirred, e.g. with a gate stirrer. Sucroselaurate is effective in stirred crystallization as well as in quiescentcrystallization.

The stearin and olein phases may be separated by filtration but for aneffective separation of the solid from the liquid phase the higherpressures of a membrane filter press are used. Suitable pressures are3-50 bar, exerted for about 20-200 minutes. However, the inventionallows a low or moderate pressure. As a rule with a pressure of 6-12 barit takes about 30-60 minutes to get a proper separation of the stearinphase from the olein phase.

The solids content of the crystal slurry before separation and of thestearin phase obtained after separation is measured according to theknown pulse NMR method (ref. Fette, Seifen, Anstrichmittel 1978, 80, nr.5, pp. 180-186).

The effect of the invention is believed to be caused by alteration ofthe crystal structure or crystal habit of the stearin under theinfluence of the additive. These might interfere in different ways withthe growth of the various crystal faces.

At microscopic inspection (see FIG. 1B) the effect of the additive isthat the crystals and crystal aggregates formed in the oil areconspicuously different from the crystals obtained without thecrystallization modifying substance (FIG. 1B). Instead of brittleneedle-like crystals, large and non-porous spherulites are formed. Sincea stearin fraction with such crystals retains less of the oleinfraction, even at low or moderate filtration pressure, the alteredcrystallization results in a considerable increase of the separationefficiency and facilitates stirred crystallization.

Although the invention is useful for solvent fractionation or detergentfractionation, the process is carried out preferably as a dryfractionation process.

The sucrose laurate is suitably applied in an amount of 0.005-2 wt. % onthe total amount of oil. A useful amount is about 1 wt. %.

The invention is illustrated by the following examples:

EXAMPLES 1-2 Dry Fractionation of Palmkernel Oil

A sample was prepared containing 1000 g of palmkernel oil (neutralised,bleached, deodorised) and 10 g (1%) of sucrose polylaurate. The samplewas heated and stirred at 65° C. until completely liquefied (no solidfat content) and then slowly cooled. Crystallization proceeded in astagnant (0 rpm) mode at the chosen temperature of 23° C. until aconstant solid phase content was reached. The sample was filtered andpressed at 12 bar for 30 minutes. After filtration and pressing, thesolid phase content (SE=separation efficiency) of the cake was measuredby NMR. For comparison the fractionation was repeated with the onlydifference that no sucrose polylaurate was added.

In example 2, palmkernel oil was fractionated following the sameprocedure as described above, but in a stirred mode (5 rpm).

Table I shows the results of these fractionations, together with theenhancement of the separation efficiency caused by the addition of thehabit modifying substance.

EXAMPLES 3-9 Dry Fractionation of Lauric Oils

The dry fractionation process of example 2 is repeated with variouslauric oils and two sucrose laurates. Each experiment has been carriedout with and without crystal habit modifier. Table I indicates the SEand the relative improvements caused by the habit modifier.

The lauric oils are coconut oil (#3), an enzymatically interesterifiedmixture of 30 wt. % fractionated palmoil-stearin (POs) and 70 wt. %fractionated palmkernel-stearin: ei(30 POs/70 PKs) (#4), the same fat,only with a ratio 50/50 POs/PKs (#5), the same fat with a ratio 60/40POs/PKs (#6), the chemically interesterified mixture of 60 wt. %hydrogenated palmoil (PO58) and 40 wt. % hydrogenated palmkernel (PK39):in (60PO58/40PK39) (#7) and the chemically interesterified mixture of 25wt. % fully hydrogenated soybean oil (BO65) and 75 wt. % coconut oil(CN): in (25BO65/75CN) (#8).

Example 9 repeats example 5 but a sucrose polyester is used and whichcontains 75 wt. % esterified laurate and 25 wt. % esterified palmitate.

The results of Table I show that the addition of sucrose polylaurate tothe fractionation of a lauric oil leads to a considerable increase ofthe separation efficiency.

                  TABLE I    ______________________________________                                    c    SE     δ    #   fat        CHM         rpm  wt. %                                         wt. %  (%)    ______________________________________    1   PK         sucrose     0    0.0  46     +59                   polylaurate      1.0  73    2   PK         sucrose     5    0.0  n.d..sup.1                                                ++                   polylaurate      1.0  71    3   CN         sucrose     5    0.0  28     +71                   polylaurate      1.0  48    4   ei(30POs/  sucrose     10   0.0  58     +12        70PKs)     polylaurate      1.0  65    5   ei(50POs/  sucrose     10   0.0  63     +19        50PKs)     polylaurate      1.0  75    6   ei(60POs/  sucrose     10   0.0  61     +15        40PKs)     polylaurate      1.0  70    7   in(60PO58/ sucrose     32   0.0  63     +8        40PK39)    polylaurate      1.0  68    8   in(25BO65/ sucrose     10   0.0  49     +10        75CN)      polylaurate      1.0  54    9   ei(50POs/  sucrose     10   0.0  63     +6%        50PKs)     polyester        1.0  67                   (75% laurate                   25% palmitate)    ______________________________________

                  TABLE II    ______________________________________    Comparative examples                                    c     SE   δ    #    fat       CHM         rpm  wt. % wt. %                                               (%)    ______________________________________    A    mfPOs     sucrose     40   0.0   68   0                   polylaurate      1.0   68    B    ei(40BO/  sucrose     30   0.0   74   -19         60BO65)   polylaurate      1.0   60    C    ei(50POs/ sucrose     10   0.0   63   0         50PKs)    polystearate     1.0   63    D    ei(50POs/ sucrose     10   0.0   63   -14         50PKs)    trilaurate       1.0   54    E    ei(50POs/ inulin      10   0.0   63   -22         50PKs)    polylaurate      0.1   49    F    ei(50POs/ sucrose     10   0.0   63   -14         50PKs)    polypalmitate    1.0   54    G    ei(50POs/ sucrose     10   0.0   63   -10         59PKS)    polyester        1.0   57                   (25% laurate                   35% palmitate                   40% stearate)    ______________________________________

Tables I and II:

    ______________________________________    c in wt. %   concentration of crystal habit modifier    rpm          stirrer rotation speed    SE in wt. %  separation efficiency    n.d.         not done, separation impossible    δ in % enhancement SE relative to blank    ______________________________________

If not mentioned specifically, the esterification degree ofsucrose-esters is 5-6.

Comparative Examples A-G

Example 2 is repeated but either with a non-lauric fat or with anadditive different from the afore-defined sucrose laurate. The SE couldnot be improved and in most cases even was lowered.

The tried non-lauric oils are double stage dry fractionated palmoilstearin (mfPOs) (#A) and an enzymatically interesterified mixture of 40wt. % soybean oil (BO) and 60 wt. % hydrogenated soybean oil (BO65),denoted as ei(40BO/60BO65) (#B).

The deviant additives are used with the enzymatically interesterifiedmixture of 50 wt. % fractionated palmoil stearin (POs) and 50 wt. %fractionated palmkernel stearin (PKs) of example 5. The additives aresucrose polystearate (#C), sucrose trilaurate (#D), which is a sucroseester with a maximum esterification degree of 3, inulin polylaurate(#E), which is a polysaccharide ester of lauric acid, sucrosepolypalmitate (#F) and a sucrose polyester (#G) which contains only 25wt. % of laurate and further palmitate (35 wt. %) and stearate (40 wt.%). The fractionation results of these comparative examples are shown inTable II.

It appears that with non-lauric oils the separation efficiency cannot beimproved when sucrose polylaurate is added. It also shows that noimproved fractionation of lauric oils is obtained with a sucrosepolyester other than the afore-defined sucrose polylaurate.

We claim:
 1. A dry fractionation process for fractionating a lauric oilwith improved separation of solid fatty material from partiallycrystallised lauric oil, which comprises the steps:a. heating the oiluntil no longer a substantial amount of solid triglyceride is present inthe oil, b. cooling and crystallising the triglyceride oil resulting ina solid stearin phase besides a liquid olein phase and c. recovering thestearin phase by separating it from the olein phase,where beforecrystallization starts a crystallization modifying substance is added tosaid triglyercide oil or to a solution of said triglyceride oil in aninert solvent, characterized in that the crystallization modifyingsubstance is a sucrose laurate having an average esterification degreeof 50-100% and a lauric acid content which is 40-100 wt. % of the totalfatty acid content.
 2. Process according to claim 1, characterised inthat the sucrose laurate has a lauric acid content which is 60-100 wt. %of the total fatty acid content.
 3. Process according to claims 1 or 2,characterised in that the sucrose laurate is used in an amount of0.005-2 wt. % on the total amount of oil.
 4. Process according to claim1 characterised in that the crystallization proceeds in a stirred mode.5. Process according to claim 1 characterised in that the lauric oil isa triglyceride oil or a mixture of triglyceride oils having a content oflauric acid which is 10-75 wt. % calculated on total fatty acid content.6. Process according to claim 5, characterised in that the lauric oil ispalmkernel oil or coconut oil.
 7. A process according to claim 2 whereinthe sucrose laurate has a lauric acid content of 75-100 wt. % of thetotal fatty acid content.
 8. Process according to claim 5 wherein thelauric oil is a triglyceride oil or mixture of triglyceride oils havinga content of lauric acid which is 30-60 wt. % calculated on total fattyacid content.